The role of polymers in the medical industry is rapidly growing. Polymers have seen use in surgical adhesives, sutures, tissue scaffolds, heart valves, vascular grafts and other medical and surgical products. One area that has seen noteworthy growth is implantable medical devices. Biocompatible polymers are particularly useful for manufacturing and coating implantable medical devices. Biodegradable biocompatible polymers suitable for coating and constructing medical devices generally include polyesters such as polylactide, polyglycolide, polycaprolactone, their copolymers or cellulose derivatives, collagen derivatives.
Properties advantageous for polymers used for medical devices include biocompatibility and, in some applications, biodegradability. The merits of biocompatible polymers include decreased inflammatory response, decreased immunological response and decreased post-surgical healing times. Biodegradability is advantageous for implanted medical devices since, in certain circumstances, the medical device would otherwise require a second surgery to remove the device after a period of time. Polymers can be rendered biodegradable biocompatible by modifying the monomer composition. In one example, an adhesive composition for surgical use was made biodegradable by copolymerizing caprolactone, ethylene glycol and DL lactic acid (see, for example, U.S. Pat. No. 6,316,523).
Additionally, polymers are used to deliver drugs from an implantable medical device made of another material wherein the polymer is coated on at least one surface of the medical device, thereby allowing for controlled drug release directly to the implantation site. Hydrophobic polymers including polylactic acid, polyglycolic acid and polycaprolactone are generally compatible with hydrophobic drugs. Hydrophilic polymers conversely are more compatible with hydrophilic drugs.
Implanted medical devices that are coated with biodegradable biocompatible polymers offer substantial benefits to the patient. Reduced inflammation and immunological responses promote faster post-implantation healing times in contrast to uncoated medical devices. Polymer-coated vascular stents, for example, may encourage endothelial cell proliferation and therefore integration of the stent into the vessel wall. Loading the coating polymers with appropriate drugs is also advantageous in preventing undesired biological responses. For example, an implanted polylactic acid polymer loaded with hirudin and prostacyclin does not generate thrombosis, a major cause of post-surgical complications (Eckhard et al., Circulation, 2000, pp 1453-1458).
There is therefore a need for improved polymeric materials suitable for drug delivery from implantable medical devices.